Operant conditioning involves learning from consequences of behaviour. If a behaviour produces a pleasant consequence, it’s likely to be repeated (reinforced). If a behaviour produces an unpleasant consequence (punishment) its less likely to be repeated. Operant conditioning can explain why babies cry for comfort - an important behaviour in building attachment. Crying leads to a response from the caregiver - feeding, comfort. As long as the caregiver provides the correct response, crying is reinforced.